Question: Some cars were parked in the grocery store parking lot. 6 more cars park at the grocery store. Now there are 15 cars in the parking lot. How many cars were parked at the grocery store at the beginning?
Answer: The number of cars parked at the store at the beginning is the difference of the number parked now and the number that came and parked earlier. The difference is $15 - 6$ cars. $15 - 6 = 9$ cars.